The invention relates to a gas-cooled machine, in particular an electrical machine, for example a turbo-generator.
EP 0 544 023 B1 discloses a gas-cooled, electrical machine of this type that comprises a rotatably drivable shaft, on which is positioned an axial ventilator. The known machine also has a cover that divides an inflow chamber from an outflow chamber. In addition, a cylindrical channel section that is positioned coaxially to the axial ventilator and surrounds the latter radially is constructed on this cover. In particular in gas-cooled turbo-generators, a cooling is ensured by means of axial ventilators that usually are attached on both sides of the turbo-generator rotor shaft and provide the required cooling gas amount and a sufficient pressure level. In such turbo-generators, cooling gas guides are constructed in front of and behind the axial ventilator, said cooling gas guides creating in connection with given rotating direction an inflow swirl in the rotating or counter-rotating direction. Because of given installation conditions, the introduction of the cooling gas into the inflow chamber, and thus the flow towards the axial ventilator, usually takes place in turbo-generators only from one side, for example from the bottom, from coolers positioned below the machine. This unilateral, i.e. asymmetrical cooling gas supply and the rotating direction of the axial ventilator causes the blades of the axial ventilator to be subjected in part to a co-swirl and in part to a counter-swirl. Under these conditions, different air speeds occur in the outflow chamber, resulting in an uneven cooling effect. However, poor cooling has a detrimental effect on the utilization of the machine.
In the known machine, the cooling, and therefore the utilization of the machine, is improved in that upstream from the axial ventilator an annular gas guidance element is positioned, which is provided with radially/axially extending guide vanes distributed over its entire circumference. In addition, a cover is provided on a portion of the outer circumference, said cover throttling the flow cross-section for the cooling gas flowing through the gas guidance element in the main direction of the inflow. By means of these guide vanes, the inflow swirl can be reduced, which has a positive effect on the efficiency and therefore on an even pressure generation of the axial ventilator. However, the production and installation of such a gas guidance element is relatively complicated and expensive.
The present invention relates to the objective of providing a different embodiment for a gas-cooled machine of the initially mentioned type, said embodiment also enabling improved cooling and therefore increased utilization of the machine, and at the same time can be produced at a relatively low cost.
The invention is based on the general idea of realizing a radial throttling gap by way of a special design of the inflow chamber in the area of an inflow opening of the channel segment directly at the inflow opening, which throttling gap extends, in particular rotation-symmetrically, along the entire inflow opening. Since the throttling effect of a throttling point depends on the pressure conditions present, higher inflow speeds are reduced to a greater degree than lower inflow speeds. The pressure conditions and the flow speeds along the throttling gap, and therefore along the inflow opening, are therefore homogenized. Overall, the blades of the axial ventilator therefore can be supplied more evenly with the inflowing cooling gas, so that the cooling effect within the machine, and therefore its utilization, can be improved. This conversion of the asymmetrical cooling gas supply that flows into the inflow chamber to a symmetrical cooling gas flow towards the axial ventilator is achieved with relatively simple constructive means, so that the invention can be realized at a relatively low cost.
In a special embodiment, the annular collar set into the annular chamber can be formed by the channel segment itself or by a portion of the channel segment. This design therefore does not require any additional components that must be installed into the machine in order to realize the machine according to the invention.
It is preferred that an inflow funnel having a curvature radius R that is smaller than the radial length HS of the blades of the axial ventilator is constructed at the inflow opening. It was found to be particularly advantageous if the ratio of R to HS is chosen greater or equal to 0.3. A ratio of R to HS in a range from about 0.3 to about 0.4 is preferred.
Advantages are also realized if an axial length b of the annular chamber, which is formed at least in the region of the inflow opening in the inflow chamber, is at least twice as large as an axial length a of the throttling gap constructed at the inflow opening. A ratio of b to a in a range from about 2.0 to about 4.5 is hereby preferred.
Additional tests also showed that it is advantageous to select the axial length a of the throttling gap smaller than the radial length HS of the blades of the axial ventilator. A ratio of a to HS in a range from about 0.35 to about 1.5 is hereby preferred.
Other important characteristics and advantages of the device according to the invention are found in the secondary claims, the drawing, and related descriptions of the FIGURES in reference to the drawing.